The terms of service for reddit are based on California law. Based on liberal Laws of California, I would venture to guess that there is some grounds for back pay. I was wondering about this with all the discussion around volunteer moderators.
Similar to Uber drivers, the test for independent contractors is pretty difficult to meet in California nowadays. So I believe there is a solid case (cough class action cough). Fuck reddit. They deserve all the backlash and a mod class action for backpay would be legendary.